Mishneh Torah — Negative Mitzvot מצוות לא תעשה, Chapter 250
The full Hebrew text of Mishneh Torah, Negative Mitzvot, Chapter 250, with English translation by Maimonides (Rambam).
שלא יונה במקח וממכר, שנאמר "אל תונו, איש את אחיו" (ויקרא כה,יד).
Not to cheat in business, as [Leviticus 25:14] states: "One man should not cheat his brother."